THE NEW WOELD MONKEYS 45 The Brain (fig. 12c).—When the brain of a Platyr-rhine monkey is compared with that of a Lemur it will be seen that it is more voluminous; and Professor Elliot Smith pointed out that the brain of Pitliecia is more than three times as large as that of a Loris with the same weight of body (149). There are, however, well-marked affinities between them. The olfactory bulbs are relatively smaller than in the Lemuroidea, and the cerebrum overlaps the cerebellum to a greater extent. In the Squirrel Monkeys (CJirysothrijc) the extent to which the cerebrum overlaps the cerebellum is very great. According to Professor Elliot Smith (148) the overlapping in Chrysothrix is " unsurpassed even in Man." The central sulcus (C.8.) is better marked in the Cebidae than in the Lemuroidea; and the Sylvian fissure (L,S.) may be separate from the intraparietal sulcus (I-P.S.) as in the other Anthiroporaorphae, or it may fuse with it as in many Lemuroidea. In the Hapalidse a separate intraparietal sulcus may not exist. The parallel sulcus (P.S.) is well marked in the Cebidse, but may be faint in the Hapalidse. The inferior frontal sulcus or sulcus rectos (S.R) is present on many hemispheres, but the inferior precentral sulcus or sulcus arcuatus (P-C.S.) varies; it may be absent, it may curve round the sulcus rectus, or it may be united to the latter to form a radiating system as in Lagothrix. On the mesial aspect of the hemisphere the calcarine sulcus (Ca.S.1) is seen to be entire or bifid, and the single calloso-marginal sulcus (C-M.S.) stops short of the parieto-occipital sulcus (P-O.S.). The collateral sulcus may be single or multiple.